EasyTreesAI interview only
Minimum Depth of Binary Tree
Asked atamazonmetamicrosoftgooglebloomberg
01 · Problem
Given the root of a binary tree, find its minimum depth: the number of nodes along the shortest path that starts at the root and ends at a leaf (a node with no children).
Return 0 for an empty tree. The tree is given in level-order, with null marking a missing child. Note that a node with only one child is not a leaf, so a path cannot stop there.
02 · Examples
Example 01
3
/ \
9 20
/ \
15 7Input
root = [3,9,20,null,null,15,7]
Output
2
Node 9 is a leaf at depth 2, which is shallower than leaves 15 and 7 at depth 3.
Example 02
Input
root = [2,null,3,null,4,null,5,null,6]
Output
5
The tree is a chain leaning right; the only leaf is 6, five nodes from the top.
Example 03
Input
root = []
Output
0
An empty tree has depth 0.
03 · Constraints
- 01The number of nodes in the tree is in the range [0, 100].
- 02-1000 <= Node.val <= 1000
- 03A leaf is a node whose left and right children are both null.
- 04The tree height is at most 100, and the tree may be fully skewed.
04 · Optimal complexity
- Time
- O(n)
- Space
- O(n)
05 · Two ways to work on it
Practice it alone or rehearse it as an interview.
Practice Mode gives you an editor and test runs, nothing else. AI Interview Mode puts a voice interviewer on the other side, adds a clock, and ends with a scored summary of the round.